1. Field of the Invention
The present invention relates to laminated capacitors, printed circuit boards, decoupling circuits, and high-frequency circuits, and more particularly, to laminated capacitors advantageously applicable to high-frequency circuits, and to printed circuit boards, decoupling circuits, and high-frequency circuits all including the laminated capacitors.
2. Description of the Related Art
A conventional laminated capacitor related to the present invention is, for example, described in Japanese Unexamined Patent Application Publication No. 11-144996 (patent reference 1). FIG. 7 is a plan view showing the appearance of a laminated capacitor 1 described in patent reference 1.
The laminated capacitor 1 is provided with a rectangular parallelepiped capacitor body 2. The capacitor body 2 has two rectangular main surfaces 3 and 4 opposing each other, and two side surfaces 5 and 6 opposing each other and extending in a longer-side direction of the main surfaces 3 and 4, and two end surfaces 7 and 8 opposing each other and extending in a shorter-side direction of the main surfaces 3 and 4, the side surfaces and the end surfaces connected to the main surfaces 3 and 4.
The capacitor body 2 is provided with a plurality of dielectric layers 9 extending in the direction of the main surfaces 3 and 4, and is also provided inside thereof with at least a pair of the first and the second internal electrodes, not shown in the figure, facing each other across a specific dielectric layer 9 in order to define a capacitor unit. The first and the second internal electrodes respectively have the first and the second lead electrodes extending onto the side surfaces 5 and 6 and the end surfaces 7 and 8 of the capacitor body 2.
On the side surfaces 5 and 6 and the end surfaces 7 and 8 of the capacitor body 2, the first external terminal electrodes 10 electrically connected to the first internal electrode through the first lead electrodes, and the second external terminal electrodes 11 electrically connected to the second internal electrode through the second lead electrodes are provided. To distinguish more easily the first external terminal electrodes 10 from the second external terminal electrodes 11, the first external terminal electrodes 10 are shown in white, and the second external terminal electrodes 11 are shown in black in the figure.
Two first external terminal electrodes 10 are provided on each of the side surfaces 5 and 6, and one first external terminal electrode 10 is provided on each of the end surfaces 7 and 8. Two second external terminal electrodes 11 are disposed on each of the side surfaces 5 and 6 so as to be disposed alternately with the first external terminal electrodes 10, and one second external terminal electrode 11 is disposed on each of the end surfaces 7 and 8 so as to be disposed alternately with the first external terminal electrode 10.
In the laminated capacitor 1 shown in FIG. 7, since the first external terminal electrodes 10 and the second external terminal electrodes 11 are adjacent to each other over the side surfaces 5 and 6 and the end surfaces 7 and 8, all the first external terminal electrodes 10 and all the second external terminal electrodes 11 are disposed alternately through the two side surfaces 5 and 6 and the two end surfaces 7 and 8.
FIG. 7 also shows typical paths and directions of current flowing through the laminated capacitor 1 by arrows. As indicated by the arrows, the current flows from the first external terminal electrodes 10 to the second external terminal electrodes 11 at the state or the point of time of the figure.
When the current flows in that way, magnetic flux having a direction determined by the direction of the current is generally induced, and therefore, a self-inductance is generated. In this case, in close vicinity of external terminal electrodes 10 and 11, the current flows away from the first external terminal electrodes 10 toward the second external terminal electrodes 11. So the directions of the current are opposite between adjacent external terminal electrodes 10 and 11, and therefore the magnetic flux is effectively canceled. As a result, the equivalent series inductance (ESL) of the laminated capacitor 1 is reduced, and therefore, the laminated capacitor 1 can be advantageously applied to high-frequency circuits.
As shown in FIG. 7, an end surface pitch Pe which defines the interval between adjacent first and second external terminal electrodes 10 and 11 disposed on the end surfaces 7 and 8 is made equal to a side surface pitch Ps defining the interval between adjacent first and second external terminal electrodes 10 and 11 disposed on the side surfaces 5 and 6 in the conventional laminated capacitor 1.
The effect of magnetic-flux cancellation, described above, between adjacent first and second external terminal electrodes 10 and 11 depends on the magnitudes of the pitches Pe and Ps. The smaller the pitches Pe and Ps are, the larger the effect of magnetic-flux cancellation is. Therefore, when the end surface pitch Pe is equal to the side surface pitch Ps as in the laminated capacitor 1 shown in FIG. 7, the effect of magnetic-flux cancellation between adjacent first and second external terminal electrodes 10 and 11 disposed on the end surfaces 7 and 8 is substantially equal to the effect of magnetic-flux cancellation between adjacent first and second external terminal electrodes 10 and 11 disposed on the side surfaces 5 and 6.
Under this condition, since the number of the first and the second external terminal electrodes 10 and 11 disposed on the end surfaces 7 and 8 is smaller than the number of the first and the second external terminal electrodes 10 and 11 disposed on the side surfaces 5 and 6 in the laminated capacitor 1 shown in FIG. 7, the effect of magnetic-flux cancellation works at fewer locations on the end surfaces 7 and 8. The effect of magnetic-flux cancellation on the end surfaces 7 and 8 is consequently expected to be inferior to that on the side surfaces 5 and 6. Therefore, if the effect of magnetic-flux cancellation on the end surfaces 7 and 8 is made stronger, the ESL of the laminated capacitor 1 can be further reduced.
In order to overcome the problems described above, preferred embodiments of the present invention provide a laminated capacitor having a greatly reduced ESL.
In addition, preferred embodiments of the present invention provide a printed circuit board, a decoupling circuit, and a high-frequency circuit all including such a novel laminated capacitor.
A laminated capacitor according to a preferred embodiment of the present invention includes a substantially rectangular capacitor body having two opposite main surfaces, and two opposite side surfaces connected to the main surfaces and extending in a longer-side direction of the main surfaces, and two opposite end surfaces connecting the main surfaces and extending in a shorter-side direction of the main surfaces.
The capacitor body includes a plurality of dielectric layers extending in the direction of the main surfaces, and at least a pair of the first and the second internal electrodes facing each other across a specific dielectric layer to define a capacitor unit. The first and the second internal electrodes respectively include the first and the second lead electrodes extending onto the side surfaces and the end surfaces of the capacitor body.
The first external terminal electrodes electrically connected to the first internal electrode through the first lead electrodes and the second external terminal electrodes electrically connected to the second internal electrode through the second lead electrodes are disposed on the side surfaces and the end surfaces of the capacitor body.
At least two first external terminal electrodes are disposed on each of the side surfaces and at least one first external terminal electrode is disposed on each of the end surfaces.
At least two second external terminal electrodes are disposed on each of the side surfaces so as to be arranged alternately with the first external terminal electrodes and at least one second external terminal electrode is disposed on each of the end surfaces so as to be disposed alternately with the first external terminal electrode.
The number of the first and the second external terminal electrodes disposed on the side surfaces is larger than that of the first and the second external terminal electrodes disposed on the end surfaces.
To solve the above-described technical problems, the laminated capacitor of various preferred embodiments of the present invention having the above-described structure has a feature in which an end-surface pitch defining the interval between adjacent first and second external terminal electrodes disposed on the end surfaces is equal to or less than about 0.9 times of a side-surface pitch defining the interval between adjacent first and second external terminal electrodes disposed on the side surfaces.
In another preferred embodiment of the present invention, an end-surface pitch defining the interval between adjacent first and second lead electrodes electrically connected to the first and the second external terminal electrodes disposed on the end surfaces is equal to or less than about 0.9 times of a side-surface pitch defining the interval between adjacent first and second lead electrodes electrically connected to the first and the second external terminal electrodes disposed on the side surfaces.
The features in the above-described preferred embodiments of the present invention may be combined. More specifically, the end-surface pitch of the lead electrodes may be equal to or less than about 0.9 times of the side-surface pitch of the lead electrodes, while the end-surface pitch of the external terminal electrodes is equal to or less than about 0.9 times of the side-surface pitch of the external terminal electrodes.
The smaller ratio of the end-surface pitch to the side-surface pitch is set, such as about 0.8 times or smaller, or further, about 0.6 times or smaller, the more advantageous it is in order to enhance the effect of magnetic-flux cancellation. On the other hand, when a smaller ratio is used, the interval between adjacent first and second external terminal electrodes becomes small, which may cause an electric short circuit. Therefore, when the ESL is reduced according to preferred embodiments of the present invention, it is preferred that the end-surface pitch be set as small as possible such that an electric short circuit does not occur between adjacent first and second external terminal electrodes.
In preferred embodiments of the present invention, it is preferred that all the first external terminal electrodes and all the second external terminal electrodes be arranged alternately along the two side surfaces and the two end surfaces.
A laminated capacitor according to a preferred embodiment of the present invention is advantageously used as a decoupling capacitor connected to a power-supply circuit for an MPU chip provided for a micro-processing unit.
Preferred embodiments of the present invention can also be applied to a printed circuit board upon which the above-described laminated capacitor is mounted.
As described above, when preferred embodiments of the present invention are applied to a printed circuit board, in another specific preferred embodiment, an MPU chip provided for a micro-processing unit is further mounted on the printed circuit board.
Preferred embodiments of the present invention can also be applied to a decoupling circuit provided with the above-described laminated capacitor.
Preferred embodiments of the present invention can further be applied to a high-frequency circuit provided with the above-described laminated capacitor.
As described above, in a laminated capacitor according to various preferred embodiments of the present invention, an end-surface pitch which defines the interval between adjacent first and second external terminal electrodes disposed on the end surfaces of the body of the capacitor is equal to or less than about 0.9 times of a side-surface pitch which defines the interval between adjacent first and second external terminal electrodes disposed on the side surfaces. Altematively, an end-surface pitch which defines the interval between adjacent first and second lead electrodes electrically connected to the first and the second external terminal electrodes disposed on the end surfaces is equal to or less than about 0.9 times of a side-surface pitch which defines the interval between adjacent first and second lead electrodes electrically connected to the first and the second external terminal electrodes disposed on the side surfaces. Therefore, the following advantages can be obtained.
The effect of magnetic-flux cancellation is greatly improved in the vicinity of the end surfaces, where a smaller number of external terminal electrodes are disposed. In addition, since the pitch between the first and the second external terminal electrodes is smaller on the side of the end surfaces, shorter than the side surfaces, current paths generated between the first and the second external terminal electrodes adjacent astride the end surfaces and the side surfaces are not very long. Therefore, the ESL of the whole laminated capacitor is effectively reduced.
Thus, the resonant frequency of the laminated capacitor can be made higher. This means that the laminated capacitor functions as a capacitor in a higher frequency band. Therefore, a laminated capacitor according to preferred embodiments can be used in electronic circuits operating in higher frequencies, and can be advantageously used, for example, as a bypass capacitor or a decoupling capacitor in high-frequency circuits.
Decoupling capacitors used in micro-processing units (MPUs) are required to function as a quick power supply. Since a laminated capacitor according to preferred embodiments of the present invention is effectively made to have a very low ESL, when the laminated capacitor is used for such a purpose, it provides a sufficiently quick response.
In preferred embodiments of the present invention, when all the first external terminal electrodes and all the second external terminal electrodes are disposed alternately along the two side surfaces and the two end surfaces, the effect of magnetic-flux cancellation is greatly improved, which is effective in reducing the ESL.
Other features, elements, characteristics and advantages of the present invention will become more apparent form the following detailed description of preferred embodiments with reference to the attached drawings.